Abstract: Thermal control systems operating under periodic outdoor ambient conditions have numerous important applications in the industrial fields, and reducing system energy consumption and enhancing temperature control effects are key to their performance improvement. Therefore, the influences of phase change material (PCM) in the envelope of a thermal control system on thermal control effects were studied by means of experiment and simulation. The results of the typical meteorological day show that, compared with polystyrene, PCM can significantly reduce system energy consumption (by 754%), surface temperature fluctuation (by 761%) and axial temperature difference (by 569%) of the object in Guangzhou. In Nanjing and Turpan, the surface temperature fluctuation can be reduced by 413% and 306% respectively, no improvement is observed in system energy consumption and axial temperature difference. The results of the typical meteorological year indicate that PCM also exhibits the advantages of thermal control in Guangzhou, but thermal control effects are strongly dependent on the temperature control setpoint, phase change range and the fluctuation of the ambient temperature. When the phase change range of the selected PCM covers the setpoint and the fluctuation range of the ambient temperature, PCM can maximize thermal control effects.